The present invention relates to an elevator hoisting apparatus, and more particularly to an elevator hoisting apparatus utilizing a parallel shaft type gear arrangement exhibiting superior low-noise and low-vibration characteristics.
In the field of elevator hoisting apparatus for driving an elevator car or cars, it is known that a parallel shaft type gear arrangement is used as a reduction gear assembly, for example, as disclosed in Japanese Patent Unexamined Publication No. 86586/1984.
FIGS. 5 and 6 schematically show the structure of the prior-art elevator hoisting apparatus set forth in the aforesaid publication.
The illustrated elevator hoisting apparatus includes a hoistway 1 for an elevator or elevators, a machine room 2 provided at the top of the hoistway 1, a floor 2A of the machine room 2, support frames 3A and 3B secured to the floor 2A, a machine platform 4 fixed to the respective of tops of the support frames 3A and 3B, a base 5 supported on the machine platform 4 with a rubber vibration insulator 6 interposed therebetween, an electric motor 7 mounted on the base 5, a reduction gear assembly 8 mounted on the same base 5, an input shaft 8A extending from the shaft of the electric motor 7 and a first gear 8B constituted by a helical gear fixed to the input shaft 8A, the first gear 8A being engaged with a second gear 8D fixed to an output shaft 8F.
The above elevator hoisting apparatus further includes a driving sheave 9 fixed to the output shaft 8F, a deflector-pulley support beam 10 fixed to the machine platform 4, a shaft 11 supported at its opposite ends by the deflector pulley support beam 10, a deflector pulley 12 rotatably fitted onto the shaft 11 and a main rope 13 reeved over the sheave 9 and the deflector pulley 12, one end of the main rope 13 being connected to an elevator car or cars 17 with the other end being connected to a counterweight 18. Although not particularly shown, a brake system serving to bring the car to a stop is provided at the input shaft 8A extending from the electric motor 7 into the reduction gear 8.
In the above-described elevator hoisting apparatus of the prior art, however, the brake device for bringing the car to a stop is provided at the shaft of the electric motor 7. Therefore, in the case of a high-speed elevator system, impact produced upon emergency stop greatly acts on the gear assembly together with the inertial force of the sheave 9. In consequence, an excessive load is applied to the respective gears and this lowers the safety of the entire elevator system.
Also, the sheave 9 and the second gear 8D are fixed to the output shaft 8F with the opposite ends thereof being supported by bearings 8G. However, since a long bearing interval exists between the opposite bearings, the thus-produced deflection of the output shaft 8F affects the state of engagement of the gear assembly, and thus there is a tendency for the level of noise to be increased. In order to prevent the increase in the level of noise, it has heretofore been necessary to increase the substantial diameters of the respective gears to some extent.
In addition, in order to prevent transmission of noise to the periphery of the machine chamber 2 and/or the elevator car, the reduction gear assembly 8 is required to have low-noise characteristics as compared with a reduction gear assembly of a general type. For this reason, a worm gear type of reduction gear assembly has heretofore been chiefly employed. In addition, a helical gear type of reduction gear assembly having a high transmission efficiency has recently started to be used for the sake of saving of energy. However, while such helical gear type reduction gear assembly affords a high transmission efficiency, the state of engagement of helical gears utterly differs from that of the worm gear type. Therefore, as mentioned in Japanese Utility Model Unexamined Publication No. 151371/1982, if the level of noise is to be reduced, it is necessary to prepare a gear with a high precision capable of satisfying the requirements of the first or higher class specified under the Japanese Industrial Standard and this leads to the problem that the production cost is increased. To overcome the problem, the aforesaid publication further states that the helix angle of a helical gear is selected within the angular range of 20 to 30 degrees. This setting of helix angle acts to improve a so-called overlapping contact ratio of gears, thereby reducing the degree of fluctuations in the respective spring constants of the mating gears. In addition, such setting of helix angle acts to suitably adjust the errors of the tooth profiles, pitches and the like of individual teeth by engaging a plurality of teeth.
According to the above-described arrangement, the selection of a helix angle within the range of 20 to 30 degrees serves to reduce the acceleration of the circumferential vibration of the driving sheave 9. However, this circumferential acceleration results chiefly from vibrations as in the direction of rotation of a rotary shaft line connecting the electric motor 7 and the sheave 9. Accordingly, in order to further reduce the level of vibration noise, a high-precision helical gear must finally be used.